Electro dynamic molecular beam device

ABSTRACT

An arrangement for deflecting specified polar molecules in a molecular beam is provided whereby detection and analysis of beam content may be achieved.

Hill 5] July 3E, W73

[ ELECTRO DYNAMIC MOLECULAR BEAM [56] References Cited DEWCE UNITEDSTATES PATENTS [75] Inventor: Robert M. Hill, Palo Alto, Calif.3,578,968 5/1971 Hellwig 250/413 3,387,130 6/1968 Lacey 250/413 [73]Ass'gnee- 321 g: g ch Memo 2,808,510 10/1957 Norton 250/413 x [22]Filed: Mar. 6, 1972 Primary Examiner-William F. Lindquist 1 pp No 232 l18 Attorney-Samuel Lindenberg et al.

' [57] ABSTRACT 250/263], 223/3; An arrangement for deflecting specifiedpolar mole i sales in a molecular beam is provided whereby detec- 0 3tion and analysis of beam content may be achieved.

5' 6121.118, 3 mwm Fi ures L ,56 34 BEAM .f u- "f DETECTlON souRcECHAMBER 2 2& VA RlABLE R F V R. F SOURCE LOAD PAIENIEDJULWQH 9.749.909

,56 "-l"- =-::;*:-::f $OURCE. CHAMBER 32 40 19 so 2 2& VARIABLE b R FRF. SOURCE LOAD VACUUM PUMP ELECTRO DYNAMIC MOLECULAR BEAM DEVICEBACKGROUND OF THE INVENTION beam apparatus for accomplishing resonancespectroscopy, involves first deflecting the beam to be analyzed by astatic-nonuniform magnetic or electric field. Following this is a regioncontaining a dynamic, uniform resonance field which changes the state ofthe atom or molecule, followed by another region wherein there is asecond static-nonuniform deflecting field. When the dynamic uniformfield is at resonance for a particular atom or molecule, the subsequentdeflection by the following static deflecting fleld is changed and thenumber of atoms or molecules reaching a detector is changed.

If deflection could be produced by a nonuniform dynamic field, and thestatic deflecting fields could be eliminated, it is obvious that by suchelimination the cost of the apparatus, its complexity and probably itsaccuracy would be increased. In the usual case using static-nonuniformfields, the force on a molecule rapidly averages to zero because ofoscillation of the dipole moment. That is, the rotating dipole moment ofthe molecule will go in and out of phase with the oscillating electricfield and the net force for any finite time period, as a result is zero.Thus, no deflection is accomplished.

OBJECT AND SUMMARY OF THE INVENTION An object of this invention is toprovide'a method and means for defelecting from a molecular beam adesired molecular component thereof using only a nonuniform dynamicresonance field.

Still another object of this invention is to provide a simpler and lesscomplicated arrangement for separating a desired molecular component ofa molecular beam which is more inexpensive than those availableheretofore.

Still another object of this is the provision of an arrangement wherebythe amount that a desired molecule may be deflected from a molecularbeam is increased.

Another object of this invention is the provision of an arrangementwherein molecular ions may be deflected from a molecular beam, whichwere not thought possible heretofore.

Yet another object of this invention is the provision of a novel anduseful method and means for analyzing the composition of a molecularbeam.

The foregoing as well as other objects of this invention may be achievedin an arrangement wherein the molecular beam desired to be analyzed isintroduced into a deflecting chamber wherein there is provided a dynamicuniform electric field which oscillates at a frequency at which adesired molecular dipole can rotate. As a result, the dipole experiencesa DC component of force and is deflected appreciably in passing throughthe field region whereby a means for selecting particular molecules froma beam is achieved. The resonant field may also be magnetic to achievedesired molecular separation. This also produces state selected beamswhich lend themselves to further study.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will best be understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view of anembodiment of this invention.

FIG. 2 is a cross sectional view along the lines 2-2 of FIG. 1.

FIG. 3 is a perspective view illustrating a ridged waveguide which maybe used in this invention in place of the coaxial waveguide.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to determine whetheror not a sufficient deflection of molecules in a beam, utilizing solelya dynamic residence field can be achieved, calculations were made onboth a classical and quantum mechanical model. These indicated thatsizeable deflections can occur for quite realizeable power levels. Forexample, the classical model predicts that the deflection d is given by:

Where P is the power in watts,r the radius of the inner conductor of50-ohm coaxial deflecting chamber of length I (both in meters), and a isthe oscillating molecular dipole moment in debyes (l debye electroncharge times bohr radius). If it is assumed that 1 equals 10 10centimeters), requals r6 10 04; millimeter) and a equals 1 debye and Pequals 1 watt, then D is approximately 0.2 X 10 0.2 millimeters Thisamount of beam separation is adequate to get good discrimination fromthe main beam. The deflected beam will contain only those molecules inresonance with the applied field and may be detected in a number ofdifferent ways. FIGS. 1 and 2 illustrate one of many possible ways ofconstructing an arrangement for achieving such deflection.

In FIG. 1 beam source 10 is representative of the source of molecularbeam desired to be analyzed. This may be a gas bottle, a gas dischargetube, a chemical reaction vessel or an oven, etc. This is connected toan inlet valve 12. The inlet valve has its opposite end connected to thevacuum chamber 14. At the coupling of the inner inlet valve 12 to thevacuum chamber, there is an entrance aperture 16, which is arranged tohave its central portion blocked by a disc 18, so that a hollowcollimated molecular beam is formed.

A coaxial waveguide 20 extends outside the vacuum chamber into thevacuum chamber 14 and is insulatingly supported from the walls of thechamber by insulating supports 22, 24.

One end of the coaxial waveguide is coupled to a variable radiofrequency source 26. The other end of the coaxial waveguide is coupledto a radio frequency load 28.

The coaxial waveguide is bent in the manner shown in the drawing so thata length thereof will extend between the entrance port 16 of the vacuumchamber and an exit port 30. A portion of the coaxial waveguide which isopposite to the entrance port 16 also has an entrance port 32 which issimilar to the entrance port 16 having a disc at the center of theopening. This entrance port 32 also assists maintaining the beam hollowand collimated. The waveguide is positioned such that its centralconductor 34 is aligned with the center of the hollow molecular beam,represented by the dotted lines 36.

As shown in FIG. 2, which is a view taken along the lines 2-2 of FIG. 1,a vacuum pump 38 is coupled to the vacuum chamber 14 and serves to keepthe pressure in the various regions within the vacuum chamber low enoughso that no scattering out of the molecular beam occur. Thecross-sectional lines shown in FIG. 2 illustrate that the waveguide isprovided with slots to enable the vacuum pump to have access to the region contained therein.

The variable rf source applies pulsed or CW electro magnetic radiationwithin the coaxial waveguide 20, which passes therethrough establishingan electric field and is dissipated in the external rf load 28. Theelectric field is provided at a frequency corresponding to the resonancefrequency of the polar molecules desired to be separated from themolecular beam.

At the end of the interaction region within the waveguide, which is theregion between the entrance opening 32 and an exit opening 40, theundeflected remaining portion of the beam 34 impinges on a beam stopportion 42 of the waveguide wall, and ultimately is pumped out of theguide and chamber. However, that portion of the beam which is deflectedis deflected toward the center of the hollow beam and passes through theexit opening 40 and thereafter enters through the opening 30, into adetection chamber 44. Detection of the portion of the beam which entersthe detection chamber 44 can be done in a number of very well knownways. The molecules which enter the chamber can be ionized by anelectron beam and thereafter counted or they may be ionized and putthrough a quadruple mass filter and then counted. Since these techniquesare well known, they will not be further discussed here. What issignificant however, is that by means of the variable RF source 26, anoscillating electric field may be established within the waveguide atone of the frequencies at which molecules desired to be separated out ofthe electron beam can be made to rotate. As a result these molecules aredeflected from the remainder of the molecular beam whereby they can beseparated and identified.

FIG. 3 is a perspective view looking into one end of a ridged waveguide40. This may be used in place of the coaxial waveguide in the vacuumchamber as shown in FIG. I. The rf field is applied to the ridgedwaveguide through coaxial connections at both ends of the ridge. Thesecoaxial connections extend through the vacuum chamber walls to avariable rf source and to an rf load respectively.

The beam enters and leaves the ridged waveguide through its open ends.Pumping of this waveguide also occurs through the open ends. Thelocation within the rdiged waveguide at which the beam is aimed is thespace between the inverted V-shaped top 42 of the central wall 44 andthe opposite inverted V-notch 44, in the top wall 46 of the ridgedwaveguide. Where the beam exits the ridged waveguide there is provided abeam stop for the undeflected molecular beam. The deflected moleculesare deflected towards the ridge or the top 42 of the central wall 44.The ridged waveguide will also have slots in the side walls to enablevacuum pumping of the interior.

Unlike the coaxial waveguide, since no central conductor extends throughthe interaction region of the ridged waveguide, the molecular beam neednot be hollow and therefore the structures shown in FIG. 1 for blockingout the center of the beam may be omitted. The ridged waveguide providesan oscillating electric and magnetic field.

Accordingly, there has been shown and described herein a novel anduseful arrangement for separating a desired component for a molecularbeam which solely employs a resonant nonuniform dynamic field forachieving such separation. Greater separation is achieved than possibleheretofore whereby the usefulness of this technique for analysis isgreatly extended.

What is claimed is:

1. Apparatus for separating desired molecules from a molecular beamcomprising:

means for establishing an interaction region for said molecular beamcomprising a waveguide having a region through which said molecular beamcan pass and having an opening at one end to afford entry of saidmolecular beam into said region of said waveguide,

means for directing said molecular beam to pass through said interactionregion,

means for applying a nonuniform oscillating dynamic electric or magneticfield, oscillating at a frequency at which the molecules desired to beseparated from said molecular beam are caused to be deflected from therest of the molecular beam, and

mean for enabling said deflected molecules to pass from said interactionregion while preventing the remainder of said molecular beams frompassing from said interaction region, comprising an opening at the otherend of said waveguide positioned at a location where only said deflectedmolecules can pass therethrough.

2. Apparatus as recited in claim 1 wherein said waveguide is a coaxialwaveguide.

3. Apparatus as recited in claim 1 wherein said waveguide is a ridgedwaveguide.

4. Apparatus as recited in claim 1 where there is included a vacuumchamber through which said waveguide passes.

5. Apparatus for separating desired molecules from a molecular beamcomprising:

a vacuum chamber having one opening in one wall for affording entry forsaid molecular beam and a second opening in the opposite wall to affordexit for said desired molecule,

a waveguide having two ends external to said vacuum chamber andextending from one of said ends into said vacuum chamber to said chamberwall opening, then extending through said chamber to the second openingin the opposite wall to provide an interaction region, and thenextending outside of said vacuum chamber to the other of said two ends,

said waveguide having an entrance opening in the portion of its wallopposite said chamber wall one opening affording entry of said molecularbeam into its interaction region and having an exit opening in theportion of its wall which is opposite said second opening in said vacuumchamber wall to afford exit of said desired molecules,

a radio frequency source coupled to said one of said ward said exitopening, and

waveguide ends for establishing an electric field in a radio frequencyload coupled to said other of said said waveguide at a frequency whichwill deflect waveguide ends. desired molecules from said molecular beamto-

1. Apparatus for separating desired molecules from a molecular beamcomprising: means for establishing an interaction region for saidmolecular beam comprising a waveguide having a region through which saidmolecular beam can pass and having an opening at one end to afford entryof said molecular beam into said region of said waveguide, means fordirecting said molecular beam to pass through said interaction region,means for applying a nonuniform oscillating dynamic electric or magneticfield, oscillating at a frequency at which the molecules desired to beseparated from said molecular beam are caused to be deflected from therest of the molecular beam, and mean for enabling said deflectedmolecules to pass from said interaction region while preventing theremainder of said molecular beams from passing from said interacTionregion, comprising an opening at the other end of said waveguidepositioned at a location where only said deflected molecules can passtherethrough.
 2. Apparatus as recited in claim 1 wherein said waveguideis a coaxial waveguide.
 3. Apparatus as recited in claim 1 wherein saidwaveguide is a ridged waveguide.
 4. Apparatus as recited in claim 1where there is included a vacuum chamber through which said waveguidepasses.
 5. Apparatus for separating desired molecules from a molecularbeam comprising: a vacuum chamber having one opening in one wall foraffording entry for said molecular beam and a second opening in theopposite wall to afford exit for said desired molecule, a waveguidehaving two ends external to said vacuum chamber and extending from oneof said ends into said vacuum chamber to said chamber wall opening, thenextending through said chamber to the second opening in the oppositewall to provide an interaction region, and then extending outside ofsaid vacuum chamber to the other of said two ends, said waveguide havingan entrance opening in the portion of its wall opposite said chamberwall one opening affording entry of said molecular beam into itsinteraction region and having an exit opening in the portion of its wallwhich is opposite said second opening in said vacuum chamber wall toafford exit of said desired molecules, a radio frequency source coupledto said one of said waveguide ends for establishing an electric field insaid waveguide at a frequency which will deflect desired molecules fromsaid molecular beam toward said exit opening, and a radio frequency loadcoupled to said other of said waveguide ends.